Based on your comment, I performed a firmware update.
Result: no change.
Can you measure the vertical distance between the segments and see if it corresponds to the circumference of the drum?
29mm.
I can’t measure the drum(s) because they are partially enclosed by the mechanism.
That’s why I suggested checking the service manual, if available. I know for some of the Hewlett-Packard printers, there is a chart in the manual that lists the circumference of various cylinders in the printing path, so as to point to a probable cause.
Yeah, I did look for that. I found a lot of charts that list the diameters of the various parts of various printers, but nothing for the 2150cn/cdn.
Have you tried looking at the imaging drums?
Oh, yes. But they can’t be rotated by hand. Must be a lock on the assembly, but I can’t find it.
So that puts the diameter of the damaged part at about 9 mm - I’d say that’s too small for a drum - more likely a roller
I think I understand where this defect is coming from. I did manage to remove part of the cyan toner assembly. Underneath the toner application roller, there’s another roller that’s in direct contact with the cyan imaging drum.
In direct contact with that roller, there’s a rod that has a thin foam strip glued to it in a spiral fashion. I assume that this is for cleaning the roller in contact with the imaging drum. Here’s a photo:
I cut a thin strip of defects from a piece of paper, and laid the strip against this foam strip, and it matches perfectly:
Although I can’t measure exactly, the roller involved is about 9mm diameter, which is close to Mangetout’s suggestion.
It also makes perfect sense: that foam strip was in contact with that roller for 7 years before it was moved. and perhaps changed the surface chemistry or perhaps even the geometry (a flat spot) of that roller.
And it also explains why this defect shape is so similar on the yellow and black channels as well.
Unfortunately, I still can’t rotate any of those parts - either due to a lock on the assembly that I can’t find, or it needs high torque to move them, and I can’t make them move by hand. So I can’t clean them.
It looks as if the good news is that the imaging drum assembly that I’ve already ordered will solve all of this.
Again, thanks to everyone that helped me think about this.
Bingo!
Most drums are shipped with a “restraining bolt” that keeps any other components away from the drum until it is installed. I know that my HP color laser periodically starts up and moves everything around, presumably to ameliorate problems like this.
